Compensating for Receiver Frequency Error in Noise Estimation Processing

ABSTRACT

A receiver circuit provides improved noise estimation processing by at least partially removing receiver frequency error bias. An initial noise estimate is compensated using an error term based on the observed receiver frequency error, and the resulting compensated noise estimate can be used to improve other signal processing in the receiver. For example, the receiver may use compensated noise estimates to generate signal quality estimates, e.g., Signal-to-Interference (SIR) estimates, having improved accuracy. Additionally, or alternatively, the receiver may use the compensated noise estimates to generate RAKE combining weights having improved noise suppression characteristics. In an exemplary embodiment, the initial noise estimate is a noise correlation matrix generated from a received reference signal, e.g., pilot symbols, and the error term is an error matrix directly generated using the observed receiver frequency error and channel estimates taken from the reference signal.

RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 10/991,878,filed 18 Nov. 2004, which is a U.S. application claiming priority toU.S. provisional application Ser. No. 60/580,202, filed 16 Jun. 2004.

TECHNICAL FIELD

The present application generally relates to wireless communicationnetworks, and particularly relates to noise estimation processing inwireless communication receivers.

BACKGROUND

Noise estimation represents an integral part of receiver processing inwireless communication networks. For example, many types of modernwireless communication networks use “best-effort” packet data channels,where individual users are served at the highest data rates that can besupported given the prevailing radio and network conditions. Accuratenoise estimation at the receivers is essential to the signal qualitycalculations performed at those receivers and, in turn, those signalquality calculations set the network's selection of serving data ratesfor the individual users.

If a wireless communication device operating on a best-effort channelreports an erroneously high received signal quality, the supportingnetwork may select a serving data rate that is too high for reliablereception at the device. The built-in retransmission mechanisms, such asthe use of Hybrid Automatic Repeat Requests (H-ARQ), commonly adoptedfor such best-effort channels exacerbate the problems associated withselecting serving data rate that is too high for reception conditions atthe receiver, because the repeated retransmission of data packeterroneously received at the device lowers the effective datatransmission rate. Indeed, with a high incidence of reception errors atthe device, the effective data rate can be significantly lower thanwould be achieved by selecting a lower data rate more commensurate withthe actual received signal quality at the device.

Conversely, if the device reports an erroneously low received signalquality, the network selects a lower data rate than actually could besupported, and the best-effort channel is underutilized with respect tothat device. The underutilization can be severe, depending upon theparticular data rate setting method adopted by the network. In W-CDMAsystems, mobile stations engaged in high-rate packet data services withthe network, e.g., High Speed Downlink Packet Access (HSDPA) services,provide received signal quality feedback to the network in the form oftransmitted Channel Quality Indicators (CQI).

Basically, the CQI reports from a given mobile station correspond to thesignal-to-interference ratio (SIR) as measured by the mobile station fora reference channel signal transmitted from the network sector servingthe mobile station. The CQI values reported by the mobile stations are“mapped” into a table of available data rates, and a mobile station thatis under-reporting signal quality is thus allocated a lower data ratethan its conditions can support.

Receiver frequency error represents a primary source of noise estimationerrors. For example, accurate noise estimation at the receiver dependson accurately processing a received reference signal, e.g., receivedpilot symbols. Any error between the receiver's frequency and the(network) transmitter's frequency gives rise to symbol de-rotationerrors, which in turn, cause noise and channel estimation errors at thereceiver. Ideally, then, a wireless communication receiver woulddirectly compensate its noise estimation processing based on observedreceiver frequency errors.

SUMMARY

The present invention comprises a method and apparatus for improvednoise estimation in a wireless communication receiver. Moreparticularly, the present invention provides for noise estimationprocessing that incorporates an error term based on an estimate ofreceiver frequency error, which may be a relatively small residualfrequency error remaining after Automatic Frequency Correction (AFC)processing at the receiver. Thus, a receiver configured according to oneor more embodiments of the present invention generates an uncompensatednoise estimate and a corresponding error term based on the observed(residual) frequency error of the receiver, and uses them to obtain acompensated noise estimate from which the frequency error bias is atleast partially removed. That compensated (unbiased) noise estimate maythen be used to improve any number of receiver functions, such as in thegeneration of signal quality measurements having improved accuracy, orin the generation of noise and interference suppression filters havingimproved suppression performance.

In one or more embodiments, the present invention comprises a method ofimproving noise estimation processing in a wireless communicationreceiver based on generating an estimate of noise correlation for areceived signal, calculating an error term corresponding to the noisecorrelation estimate arising from a receiver frequency error, andobtaining a compensated noise correlation estimate by removing the errorterm from the noise correlation estimate. Note that with a zero meanassumption, the noise correlation estimate is expressed as a noisecovariance estimate, and it should be understood that use of the term“noise covariance” herein does not exclude the more general notion ofcomputing noise correlations where a non-zero mean is considered.

With that point in mind, a receiver may use received pilot symbols fornoise covariance estimation, or it may use any other type of referencesignal transmitted by a supporting wireless communication network toenable channel and noise estimation processing at the receiver. In aW-CDMA wireless communication network, for example, the receiver ofinterest may be comprised in a wireless communication device, and theincluded receiver circuit may use Common Pilot Channel (CPICH) symbolsfor channel and noise estimation processing.

Regardless of the particular reference signal used, the receiver may usenoise correlation estimates that are compensated for receiver frequencyerror as the basis for calculating received signal quality estimateshaving an improved accuracy. That is, the receiver improves itscalculation of signal quality estimates by wholly or partially removingthe effects of receiver frequency error bias. These improved signalquality estimates may be transmitted to an associated wirelesscommunication network in the form of CQI reports, or some other form ofsignal quality report, for use by the network in setting the data ratesat which data is transmitted to the receiver.

According to one or more embodiments of the above method of improvednoise estimation, a receiver circuit generates an initial noisecorrelation estimate as an uncompensated noise covariance matrix that isbased on a received reference channel signal and correspondingpropagation channel estimates. For example, the receiver circuit maygenerate propagation channel estimates and an uncompensated noisecovariance matrix based on processing one or more received pilotsymbols. In any case, the receiver circuit calculates the error term asan error matrix that is based on an estimate of the receiver frequencyerror and a channel correlation matrix determined from the propagationchannel estimates, which may be expressed in terms of covariance. Thereceiver frequency error may be determined by estimating the phase shiftthat occurs over a given number of pilot symbols, or by some othermeans. Regardless of the particular processing carried out for receiverfrequency error estimation, the resulting error matrix may be removedfrom the uncompensated noise covariance matrix to obtain a compensatednoise covariance matrix that can then be used for signal qualityestimation, filtering, etc.

In carrying out the above noise estimation processing, the receivercircuit can be configured as hardware, software, or any combinationthereof. As such, the present invention may be embodied in one or moreintegrated circuits, such as Application Specific Integrated Circuits(ASICs) or Field Programmable Gate Arrays (FPGAs), or in electronicdesign files for synthesizing the appropriate processing logic in suchdevices, or as stored program instructions for execution by amicroprocessor, Digital Signal Processor (DSP), or other digital logicprocessor. Further, the receiver circuit may be implemented as part of,or in association with, additional receiver circuitry, including aRAKE-type receiver that provides one or more pilot channel despreaders(correlators) to obtain received pilot symbols and a channel estimationcircuit to provide propagation channel estimates based on the despreadpilot symbols.

Thus, in at least one embodiment of the receiver circuit, it includes anoise covariance estimation circuit configured to generate a noisecovariance estimate for a received signal, and a compensation circuitconfigured to calculate an error term corresponding to the noisecovariance estimate arising from a receiver frequency error and obtain acompensated noise covariance estimate by removing the error term fromthe noise covariance estimate. The receiver circuit may further include,or be associated with a signal quality estimation circuit configured togenerate a signal quality estimate from the compensated noise covariancematrix, a frequency error estimation circuit configured to estimate thereceiver frequency error used to calculate the error term, and with theaforementioned RAKE-type receiver and channel estimation circuits.

Of course, those skilled in the art will recognize that alternativecircuit embodiments may be used, and that the above arrangement is givenby way of non-limiting example. Indeed, the present invention is notlimited by the above features and advantages, and those skilled in theart will recognize additional features and advantages upon reading thefollowing detailed description, and upon viewing the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless communication device inaccordance with one or more embodiments of the present invention.

FIG. 2 is a block diagram of receiver details for the communicationdevice of FIG. 1.

FIG. 3 is flow diagram of noise estimation processing logic inaccordance with one or more embodiments of the present invention.

FIG. 4 is a flow diagram of processing logic details for one or moreembodiments of the noise estimation processing outlined in FIG. 3.

DETAILED DESCRIPTION

FIG. 1 illustrates a wireless communication device 10 that is configuredin accordance with one or more embodiments of the present invention.Device 10 may comprise essentially any type of wireless communicationdevice or system, and thus may comprise a mobile station, a PortableDigital Assistant (PDA), a pager, a laptop/palmtop computer, etc. In atleast one embodiment, the wireless communication device 10 comprises amobile station configured for operation in a cellular communicationnetwork. In at least one embodiment, the wireless communication device10 comprises a mobile station configured for operation in a WidebandCDMA (W-CDMA) communication network.

Thus, with the understanding that device 10 is not limited by thedisclosed illustrations, FIG. 1 depicts an arrangement wherein device 10is adapted for wireless communication and comprises a receiver 12 toreceive and process received signals, a transmitter 14 to generate andtransmit signals, one or more antennas 16 coupled to receiver 12 andtransmitter 14 via a switch/duplexer 18, a system controller 20 tosupport receive/transmit operations, and to support user interface (UI)22, which may include a display, keypad, audio input/output transducers,etc.

Turning to receiver details for one or more embodiments of device 10,FIG. 2 partially illustrates the included receiver 12. In theillustrated embodiment, receiver 12 includes a radiofrequency (RF)front-end circuit 30, a RAKE-type receiver 32, a receiver circuit 34that is configured for noise estimation processing in accordance withthe present invention, and which may include, or be associated with, asignal quality estimation circuit 36, and an Automatic Frequency Control(AFC) circuit 38. In at least one embodiment of receiver circuit 34,which is of particular interest in the context of the present invention,it includes a noise covariance estimation circuit 40 configured togenerate a noise estimate for the received signal, and a compensationcircuit 42 configured to compensate the noise estimate for thereceiver's frequency error. Such error generally is measured withrespect to the transmitter frequency of the network transmitteroriginating the received signal.

The compensated noise estimate may be used by signal quality estimationcircuit 36 to generate signal quality measurements having improvedaccuracy, i.e., having the receiver frequency error bias removed or atleast reduced, and/or may be used to improve operation of RAKE receiver32. For example, some embodiments of RAKE receiver 32 may incorporatethe present invention's compensated noise correlation estimates intoRAKE combining weight generation to provide improved interference andnoise suppression. That is, a combining weight generator, whetherincluded in receiver circuit 34, or RAKE receiver 32, may be configuredto generate RAKE combining weights using the compensated noisecorrelation estimates, such that the combining weight generation isimproved by reducing the effects on receiver frequency error.

RAKE receiver 32 can be associated with a receiver RF front-end circuit30, which includes amplifiers, mixers, filters, and analog-to-digitalconverters (ADCs) as needed or desired. Front-end circuit 30 can beconfigured to provide the RAKE receiver 32 with one or more sampledsignals r′ (e.g., I/Q sample streams) corresponding to the receivedsignal r(t). Searcher 50 identifies one or more multipath components ofthe received signal arising from the time dispersive nature of multipathpropagation, and delay estimator 52 generates corresponding delayestimates. In turn, pilot channel correlator(s) 54, channel estimator56, and traffic correlator(s) 58, use those delay estimates to despreadpilot and traffic symbols, and to make propagation channel estimates.

More particularly, in Direct Sequence CDMA embodiments of receiver 12,pilot channel correlator(s) 54 are time-aligned to one or more multipathrays of the received signal, and use a corresponding despreading code(e.g., Walsh code) to despread pilot symbols contained in the receivedsignal, and channel estimator 56 uses the despread pilot symbols, whichmay be Common Pilot Channel (CPICH) symbols such as used in W-CDMAsystems, to generate propagation channel estimates for the receivedsignal. Those propagation channel estimates are used to compensate thedespread traffic channel symbols obtained from traffic correlators 58for propagation channel phase and attenuation characteristics. RAKEcombiner 60 generally improves the signal-to-noise ratio (SNR) of thereceived signal by combining the despread traffic symbols from each ofone or more multipath rays of the received signal in RAKE combiner 60.The RAKE-combined signal output by combiner 60 is then provided to adecoder and/or other processing circuits in the receiver's signalprocessing chain.

In looking at noise estimation processing with respect to the receivercircuit 34, FIG. 3 illustrates processing details for one or moreembodiments of the present invention, wherein receiver circuit 34generates an initial noise correlation estimate for the received signal(Step 100). For zero mean, the noise correlation estimate is expressedas a noise covariance estimate. It should be understood that the presentinvention contemplates a configuration of receiver circuit 34 whereinits noise estimations generally are based on performing noise covariancecalculations, but the more general noise correlation processing withnon-zero may be implemented as needed or desired.

Regardless, processing continues with the calculation of an error termfor the initial noise estimate, wherein the error term corresponds to areceiver frequency error (Step 102). In turn, the error term is used toobtain a compensated noise estimate (Step 104). More particularly, theinitial uncompensated noise estimate, which is biased by receiverfrequency error, is made into an unbiased estimate by compensating itfor the receiver frequency error. In at least one embodiment of thepresent invention, the bias in the initial noise estimate arising fromthe receiver frequency error is removed to obtain an unbiased noiseestimate by subtracting the error term from the initial (biased) noiseestimate. It should be understood that such operations are based onscalar operations where the noise estimate is a scalar value, vectoroperations where the noise estimate is a vector value, and matrixoperations where the noise estimate is a matrix value.

With the broad processing of FIG. 3 in mind, FIG. 4 illustrates noiseestimation processing details for a given noise estimation interval. Itshould be understood that receiver 12 generally maintains updated noiseestimations, which are used for periodically measuring and reportingsignal quality to a supporting wireless communication network. In W-CDMAembodiments of device 10, the update interval is typically at least asshort as 2 ms (500 Hz), which is the defined reporting interval formobile station CQI reports that are returned to the network by devicesengaged in high-rate packet data services on the HSDPA channel.

In support of noise estimation processing, receiver 12 receives anddespreads pilot symbols (or any other type of suitable reference signalinformation), and generates propagation channel estimates from them(Steps 110 and 112). Let y(k) be a vector of despread pilot signalsamples from all fingers in a RAKE receiver during the kth symbolperiod:

y(k)=s(k)h(k)m(k)+n(k),  (1)

where s(k) denotes the kth transmitted reference symbol, h(k) denotesthe true channel response at time k, m(k) is a multiplicativeimpairment, and n(k) is additive noise. For simplicity, but without lossof generality, s(k) can be set constant to “1” herein. When the receiveris subject to a residual frequency error, the multiplicative impairmentcan be expressed as

m(k)=e ^(i2πvk),  (2)

where V is a per reference symbol phase change corresponding to aresidual receiver frequency error expressed as Δf. Note that with thismethod, the receiver frequency error can be determined over a definedduration of reference (pilot) symbols.

As for the per reference symbol phase change, it holds that

v=Δf·T _(pilot),  (3)

where T_(pilot) is the duration of one reference symbol. In a W-CDMAembodiment, a CPICH reference symbol can be used, which would giveT_(pilot)=1/15000 s. By way of non-limiting example, receiver 12 maythen be configured to generate channel estimates as,

$\begin{matrix}{{\hat{h} = {\frac{1}{N}{\sum\limits_{k = 0}^{N - 1}{y(k)}}}},} & (4)\end{matrix}$

where ĥ is the estimated channel response corresponding to the truechannel response h, taken as an average over N reference symbols, e.g.,CPICH symbols.

Using the channel estimates generated above, an estimate of the noiseterm at time k can be calculated as

{circumflex over (n)}(k)=y(k)−ĥ.  (5)

With the above noise formulation, receiver circuit 34 can be configuredto calculate an initial noise covariance estimate (Step 114),{circumflex over (R)}₀, as

$\begin{matrix}{{\hat{R}}_{0} = {\frac{1}{N - 1}{\sum\limits_{k = 0}^{N - 1}{{\hat{n}(k)}{{{\hat{n}}^{H}(k)}.}}}}} & (6)\end{matrix}$

The above noise estimate is an unbiased estimate in the absence ofreceiver frequency error, but includes a frequency-related bias error tothe extent that the receiver's operating frequency mismatches the remotetransmitter's frequency. AFC circuit 38 is configured to correct grossreceiver frequency errors on an ongoing basis, but such correctionsnonetheless leave non-zero residual frequency errors that contribute tonoise estimation errors if not compensated for in noise estimationprocessing. As mentioned earlier herein, such errors can be significantbecause they cause device 10 to report a lower-than-actual receivedsignal quality to a supporting wireless network, which causes thenetwork to serve device 10 at a lower data rate than is appropriate forthe actual received signal quality at device 10.

In the presence of receiver frequency error Δf, de-rotation of thereference symbols used in the channel and noise estimation processessuffer from error in proportion to the frequency error of receiver 12.In particular, the channel estimates generated in Eq. (4) can beexpressed as

$\begin{matrix}{{\hat{h} = {{\frac{1}{N}{\sum\limits_{k = 0}^{N - 1}{y(k)}}} = {{\frac{1}{N}{\frac{1 - ^{\; 2\pi \; {vN}}}{1 - ^{\; 2\pi \; v}} \cdot h}} + {\frac{1}{N}{\sum\limits_{k = 0}^{N - 1}{n(k)}}}}}},} & \left( {7a} \right)\end{matrix}$

and the estimate of the noise term in Eq. (5) can be expressed as

$\begin{matrix}{{\hat{n}(k)} = {{{y(k)} - \hat{h}} = {{\left( {^{\; 2\pi \; {vk}} - {\frac{1}{N}\frac{1 - ^{\; 2\pi \; {vN}}}{1 - ^{\; 2\pi \; v}}}} \right) \cdot h} + {n(k)} - {\frac{1}{N}{\sum\limits_{l = 0}^{N - 1}{{n(l)}.}}}}}} & \left( {7b} \right)\end{matrix}$

With the above expressions in mind, an error term corresponding toreceiver frequency error can be expressed as

$\begin{matrix}{{{\Delta \; R} = {\frac{1}{N - 1}\left( {N - {\frac{1}{N}\frac{1 - {\cos \left( {2\pi \; {vN}} \right)}}{1 - {\cos \left( {2\pi \; v} \right)}}}} \right){hh}^{H}}},} & (8)\end{matrix}$

which can be implemented using the estimated channel response, i.e.,using the propagation channel estimates ĥ, and thus expressed as,

$\begin{matrix}{{{\Delta \; R} \approx {\left( {\frac{N\left( {N + 1} \right)}{3}\pi^{2}v^{2}} \right)\hat{h}\; {\hat{h}}^{H}}},} & (9)\end{matrix}$

where the first term in a Taylor series expansion has been used. Higherorder terms also may be included, but they are negligible for moderatefrequency errors. In error matrix form, the error term ΔR can beexpressed as a function of the observed phase change v, and theestimated channel covariance matrix given by ĥĥ^(H). In the context ofFIG. 4, then, processing continues with the calculation of the channelcovariance matrix (Step 116) and the error matrix (Step 118).

In selecting values for the above equation in the context of W-CDMAembodiments of device 10, v may be expressed as Δf/15000, where 15000CPICH symbols are received per second, and where Δf is the residualreceiver frequency error in Hz. Referring to FIG. 2, one sees that AFCcircuit 38 may provide receiver circuit 34 with an indication of theresidual frequency error as Δf, or pre-computed as v. In eitherinstance, the indication may be provided as a periodically updateddigital value for use by compensation circuit 42.

Regardless of variations in the implementation details, the presentinvention compensates for receiver frequency errors in its noiseestimation processing by directly considering the above equation. Moreparticularly, the present invention obtains a compensated noise estimateby removing a frequency-related error term from its initial noiseestimate. Set in the context provided by the above equations, thereceiver circuit 34 generates a noise covariance matrix {circumflex over(R)}₀ that includes a receiver frequency error bias, generates an errormatrix ΔR that is proportional to that frequency error, and obtains acompensated noise covariance matrix {circumflex over (R)}_(unbiased)based on removing the error matrix from the biased estimate. As such,the compensated estimate (in Step 120) may be obtained as,

$\begin{matrix}{{\hat{R}}_{unbiased} = {{{\hat{R}}_{0} - {\Delta \; R}} = {{\hat{R}}_{0} - {\left( {\frac{N\left( {N + 1} \right)}{3}\pi^{2}v^{2}} \right)\hat{h}\; {{\hat{h}}^{H}.}}}}} & (10)\end{matrix}$

Thus, in at least one embodiment of the present invention, thecompensated (unbiased) noise estimates are used for improved signalquality estimation, e.g., signal quality estimation circuitry uses thecompensated noise estimates to calculate more accurate signal qualityestimates (Step 122). Thus, the compensated noise covariance matrix,{circumflex over (R)}_(unbiased), may be used by estimation circuit 36to obtain an improved SIR estimate for the received signal, and thus toobtain an improved CQI value for reporting by device 10 to thesupporting wireless network. Note that steps 110 through 122 thus may becarried out according to the desired SIR/CQI reporting interval.However, it should be understood that the present invention contemplatesadditional or alternative uses, such as the use of compensated noiseestimates by RAKE receiver 32 to generate improved RAKE combiningweights for noise suppression with respect to received traffic channelsymbols.

In supporting signal quality reporting, AFC circuit 38 and/orcompensation circuit 42 of receiver circuit 34 may periodically updatethe residual frequency error estimate, v (Steps 124 and 126), every NCPICH symbols, or may maintain a running average of v updated as CPICHsymbols are received and despread. In either case, such processing mayrun concurrently with the noise estimation processing such that updatedfrequency error information is available as needed for compensatingongoing noise estimation processing.

With dynamically updated unbiased noise estimates thus availableaccording to a defined update interval, one may take advantage offiltering to smooth the unbiased estimates, and thus obtain what, insome cases, may be a more suitable unbiased noise estimate. Thedesirability of filtering the unbiased noise estimates and the degree offiltering applied may vary depending on the performance needs of device10, and on the computational resources and demands attendant thereto. Inany case, a filter may be implemented in receiver circuit 34 such thatit outputs a filtered version of its unbiased noise estimates. This maybe computed for example as,

{circumflex over (R)} _(filt) =α{circumflex over (R)}_(filt)+(1−α){circumflex over (R)} _(biased),  (11)

where α may be adjusted to control the filter response. For example,where 0≦α<1, then a setting close to 1 imposes heavier filtering and asetting at or close to 0 imposes lighter filtering.

In any case, SIR estimation in one or more embodiments of the presentinvention may be carried out by signal quality estimation circuit 36according to,

SINR=ĥ ^(H) {circumflex over (R)} _(unbiased) ⁻¹ ĥ,  (12)

for a “Generalized” RAKE receiver embodiment that uses noisesuppression/whitening in its RAKE combining weight generation. WhereRAKE receiver 32 is configured for consideration of noise powers only,one may obtain a Signal-to-Noise-plus-Interference Ratio (SINR) bytaking the diagonals of the unbiased noise covariance matrix thusly,

$\begin{matrix}{{{SINR} = {\sum\limits_{i}\frac{{{h(i)}}^{2}}{{\hat{r}}_{unbiased}\left( {i,i} \right)}}},} & (13)\end{matrix}$

where {circumflex over (r)}_(unbiased)(i,i) is the ith diagonal elementof {circumflex over (R)}_(unbiased). Finally, if RAKE receiver 32 doesnot incorporate noise statistics into its combining weight generation,then the SINR for the received signal is given as,

$\begin{matrix}{{{SINR} = \frac{h^{H}h}{\sigma_{I}^{2}}},} & (14)\end{matrix}$

where σ_(i) ² can be computed as,

$\begin{matrix}{{\sigma_{I}^{2} = {\frac{1}{J}{\sum\limits_{i = 0}^{J - 1}{{\hat{r}}_{unbiased}\left( {i,i} \right)}}}},} & (15)\end{matrix}$

where J denotes the total number of RAKE fingers.

With any of the above SINR computations, a corresponding CQI may begenerated based on indexing a SINR-to-CQI lookup table, or based onmaking a SINR-to-CQI calculation. For more information, refer to theco-pending U.S. application Ser. No. 10/869,527, filed on 16 Jun. 2004,and which is incorporated herein by reference. Note, too, that thefiltered version of the unbiased noise estimates may be used in any ofthe above signal quality calculations.

Those skilled in the art should appreciate that the particular method(s)adopted for channel estimation, noise covariance estimation, signalquality estimation, and CQI reporting, if implemented, may be varied asneeded or desired without departing from the scope of the presentinvention. Those skilled in the art will appreciate that should othermethods be used, the expression for the covariance matrix error term maychange correspondingly, but the methods disclosed herein remain validwith such changes. Indeed, the present invention is not limited by theforegoing discussion and accompanying illustrations, but rather islimited only by the following claims and their reasonable equivalents.

What is claimed is:
 1. A method of improving noise estimation processingin a wireless communication receiver, the method comprising: generatingan estimated noise correlation matrix for a received signal, based on apropagation channel estimate vector corresponding to a plurality ofcorrelator delays; calculating an error matrix that represents anestimate of that portion of the estimated noise correlation matrix thatarises from a receiver frequency error; and obtaining a compensatednoise correlation estimate by removing the error term from the noisecorrelation estimate.
 2. The method of claim 1, further comprisingcalculating a signal-to-interference ratio based on the compensatednoise correlation estimate.
 3. The method of claim 2, further comprisingdetermining a Channel Quality Indicator from the signal-to-interferenceratio for transmission to a supporting wireless communication network.4. The method of claim 1, further comprising determining RAKE combiningweights for a RAKE receiver circuit included in the wirelesscommunication receiver based on the compensated noise correlationestimate.
 5. The method of claim 1, further comprising determiningsignal quality estimates for the received signal based on thecompensated noise correlation estimate.
 6. The method of claim 1,wherein generating a noise correlation estimate for a received signalcomprises generating an initial noise correlation matrix based on areceived reference channel signal and corresponding propagation channelestimates.
 7. The method of claim 6, wherein calculating an error termcorresponding to the noise correlation estimate arising from a receiverfrequency error comprises calculating an error matrix based on anestimate of the receiver frequency error and a channel correlationmatrix determined from the propagation channel estimates.
 8. The methodof claim 7, wherein obtaining a compensated noise correlation estimateby removing the error term from the noise correlation estimate comprisessubtracting the error matrix from the initial noise correlation matrixto obtain a compensated noise correlation matrix.
 9. The method of claim1, wherein generating a noise correlation estimate for a received signalcomprises generating an initial noise covariance matrix based on areceived reference channel signal and corresponding propagation channelestimates generated from the received reference channel signal.
 10. Themethod of claim 9, wherein the reference channel signal is a pilotchannel signal, and wherein the propagation channel estimates aregenerated from received pilot symbols.
 11. The method of claim 10,wherein calculating an error term corresponding to the noise correlationestimate comprises calculating an error matrix based on determining anestimate of the receiver frequency error over a defined interval ofpilot symbols, and wherein obtaining a compensated noise correlationestimate by removing the error term from the noise correlation estimatecomprises subtracting the error matrix from the initial noise covariancematrix to obtain a compensated noise covariance matrix.
 12. A wirelesscommunication device comprising a receiver circuit configured to:generate an estimated noise correlation matrix for a received signal,based on a propagation channel estimate vector corresponding to aplurality of correlator delays; calculate an error matrix thatrepresents that portion of the estimated noise correlation matrix thatarises from a receiver frequency error; and obtain a compensated noisecorrelation estimate by removing the error term from the noisecorrelation estimate.
 13. The device of claim 12, wherein the receivercircuit includes a signal quality estimation circuit configured toestimate a signal quality for the received signal based on thecompensated noise correlation estimate.
 14. The device of claim 13,wherein the signal quality estimation circuit is configured to calculatea signal-to-interference ratio based on the compensated noisecorrelation estimate, such that the calculated signal-to-interferenceratio is compensated for the receiver frequency error.
 15. The device ofclaim 14, wherein the signal quality estimation circuit is configured todetermine a Channel Quality Indicator value from the calculatedsignal-to-interference ratio, such that the Channel Quality Indictorvalue is compensated for the receiver frequency error.
 16. The device ofclaim 12, wherein the receiver circuit includes or is associated with afrequency error estimation circuit configured to estimate the receiverfrequency error used to calculate the error term.
 17. The device ofclaim 16, wherein the frequency error estimation circuit is configuredto estimate the receiver frequency error based on determining a symbolphase change over a defined interval of pilot symbols in a pilot signalreceived in association with the received signal.
 18. The device ofclaim 12, further comprising a RAKE receiver operatively associated withthe receiver circuit, said RAKE receiver configured to calculate RAKEcombining weights based on the compensated noise correlation estimate,such that the RAKE combining weights are compensated for the receiverfrequency error.
 19. The device of claim 12, wherein the receivercircuit includes a noise correlation estimation circuit configured togenerate the noise correlation estimate, and a compensation circuitconfigured to calculate the error term and to obtain the compensatednoise correlation estimate.
 20. The device of claim 19, wherein thenoise correlation estimation circuit is configured to generate the noisecorrelation estimate as an initial noise covariance matrix, and whereinthe compensation circuit is configured to calculate the error term as anerror matrix based on the receiver frequency error, and to obtain thecompensated noise correlation estimate as a compensated noise covariancematrix by subtracting the error matrix from the initial noise covariancematrix.
 21. The device of claim 12, wherein the receiver circuitincludes or is associated with a RAKE-type receiver configured todespread a received reference channel signal to obtain referencesymbols, and a channel estimation circuit configured to generationpropagation channel estimates from the reference symbols, and whereinthe noise correlation estimate comprises a noise covariance matrixgenerated from the reference symbols and the corresponding propagationchannel estimates.
 22. The device of claim 12, wherein the receivercircuit is configured to generate the noise correlation estimate as anoise covariance matrix, and to obtain the compensated noise correlationestimate as a compensated noise covariance matrix based on subtractingan error matrix from the noise correlation matrix, wherein the errormatrix is based on the receiver frequency error.
 23. The device of claim12, wherein the device comprises a mobile station configured foroperation in a cellular communication network, and wherein the mobilestation is configured periodically to obtain compensated noisecorrelation estimates, and to generate and transmit Channel QualityIndicator reports to the cellular communication network based on thecompensated noise correlation estimates.
 24. The device of claim 12,wherein the device comprises a Wideband Code Division Multiple Accessmobile station configured for operation in a Wideband Code DivisionMultiple Access wireless communication network.
 25. A computer readablemedium storing a computer program for a wireless communication devicecomprising: program instructions to generate a noise correlationestimate for a received signal; program instructions to calculate anerror term corresponding to the noise correlation estimate arising froma receiver frequency error; and program instructions to obtain acompensated noise correlation estimate by removing the error term fromthe noise correlation estimate.
 26. The computer readable medium ofclaim 25, wherein the computer program comprises program instructions togenerate a signal quality estimate from the compensated noisecorrelation estimate.
 27. The computer readable medium of claim 26,wherein the computer program comprises program instructions to estimatethe receiver frequency error used to calculate the error term based onobserving symbol phase changes over a defined interval of referencechannel symbols received in conjunction with the received signal. 28.The computer readable medium of claim 25, wherein the computer programcomprises program instructions to generate propagation channel estimatesbased on despread reference symbols obtained from a received referencesignal, and wherein the program instructions to generate the noisecorrelation estimate comprise program instructions to generate a noisecorrelation matrix from the reference symbols and the correspondingpropagation channel estimates.
 29. The computer readable medium of claim25, wherein the program instructions to generate the noise correlationestimate comprises program instructions to generate a noise correlationmatrix based on a received reference channel signal and correspondingpropagation channel estimates.
 30. The computer readable medium of claim29, wherein the program instructions to calculate the error termcomprise program instructions to calculate an error matrix based on anestimate of the receiver frequency error and a channel correlationmatrix determined from the propagation channel estimates.
 31. Thecomputer readable medium of claim 30, wherein the program instructionsto obtain the compensated noise correlation estimate comprise programinstructions to obtain a compensated noise correlation matrix bysubtracting the error matrix from the noise correlation matrix.
 32. Thecomputer readable medium of claim 25, wherein the program instructionsto generate a noise correlation estimate for a received signal compriseprogram instructions to generate an initial noise covariance matrixhaving an error component arising from the receiver frequency error, andwherein the program instructions to obtain a compensated noisecorrelation estimate by removing the error term from the noisecorrelation estimate comprise program instructions to subtract an errormatrix from the initial noise covariance matrix to obtain a compensatednoise covariance matrix.
 33. The computer readable medium of claim 32,wherein the program instructions to calculate an error termcorresponding to the noise correlation estimate arising from a receiverfrequency error comprises program instructions to compute an errormatrix based on determining a pilot symbol phase change over a definedinterval of pilot symbols received in association with the receivedsignal.
 34. The computer readable medium of claim 32, further comprisingprogram instructions to compute a signal quality estimate for thereceived signal based on the compensated noise covariance matrix. 35.The computer readable medium of claim 32, further comprising programinstructions to compute RAKE combining weights for RAKE receiverprocessing of the received signal based on the compensated noisecovariance matrix.